Generally, common main objective (CMO) surgical microscopes use vertical illumination that is projected down onto a sample, nearly parallel to an observer's viewing angle. In these microscopes, glare may occur when light from the vertical illumination reflects off one surface of the microscope objective lens and couples into one of the ocular channels.
These microscopes are typically designed to reduce, or possibly prevent, reflected rays from reaching or coupling into the microscope ocular channels, thereby reducing, or possibly avoiding, glare. A combination of techniques have been used to reduce the likelihood of glare, for example, high quality coatings may be used to reduce reflection intensity; location of virtual images may be controlled by careful choice of lens curvatures and spacing; field diaphragms and baffles may be used to block reflected light that does not contribute to the microscope image and the like.